TW202347007A - Lithographic apparatus and associated methods - Google Patents

Abstract

A lithographic apparatus comprises: a plurality of optical elements defining an optical path; a first body; a second body; and a voltage supply. The lithographic apparatus may be an extreme ultraviolet (EUV) lithographic apparatus. The plurality of optical elements defining the optical path are arranged to receive a radiation beam, project the radiation beam onto a reticle so as to pattern the radiation beam and to form an image of the reticle on a substrate. The first body and second body are proximate to the optical path. The voltage supply is arranged to apply a potential difference across the first and second bodies. In particular, the first body, the second body and/or the voltage supply are arranged so as to control a flux and/or energy distribution of ions incident on the first body from a plasma formed in the optical path by the radiation beam.

Description

Lithography equipment and related methods

The present invention relates to a lithography equipment and a related method for operating the lithography equipment. In particular, the present invention relates to extreme ultraviolet (EUV) lithography equipment in which a hydrogen plasma can be formed. The present invention relates to apparatus and methods for controlling the flux and/or energy distribution of ions from a plasma incident on a body within a lithography apparatus.

Lithography equipment is a machine constructed to apply a desired pattern to a substrate. Lithography equipment may be used, for example, in the manufacture of integrated circuits (ICs). For example, a lithography apparatus may project a pattern from a patterning device (eg, a photomask) onto a layer of radiation-sensitive material (resist) provided on a substrate.

The wavelength of the radiation used by the lithography equipment to project the pattern onto the substrate determines the minimum size of the features that can be formed on that substrate. In contrast to conventional lithography equipment, which may for example use electromagnetic radiation with a wavelength of 193 nm, a lithography equipment using EUV radiation as electromagnetic radiation with a wavelength in the range of 4 nm to 20 nm may be used. Form smaller features on the substrate.

In use, the portion of the EUV lithography apparatus through which the EUV radiation propagates can be maintained at a pressure well below atmospheric pressure, for example using a container that is evacuated using a vacuum pump. It is known to provide hydrogen gas (at low pressure) in these parts of EUV lithography equipment. EUV radiation beams are usually pulsed radiation beams. As each pulse of radiation propagates through the optical path in the lithography apparatus, the gas molecules in the optical path tend to ionize causing a plasma to form in the optical path. The plasma can diffuse away from the optical path so that the plasma extends slightly outside the volume through which the radiation beam propagates.

It may be necessary to provide equipment that avoids or mitigates one or more of the problems associated with prior technologies.

According to a first aspect of the present disclosure, a lithography apparatus is provided, which includes: a plurality of optical elements defining an optical path, the plurality of optical elements being configured to receive a radiation beam and project the radiation beam to a magnification mask. for patterning the radiation beam and forming an image of the reticle on the substrate; a first body proximate the optical path; a second body proximate the optical path; and a voltage supply configured to span the first body and The second body applies a potential difference; wherein the first body, the second body and/or the voltage supplier are configured to control the flux of ions incident on the first body from the plasma formed in the optical path by the radiation beam and /or energy distribution.

The lithography equipment may be an extreme ultraviolet (EUV) lithography equipment. In use, the optical path may be maintained at a pressure well below atmospheric pressure, for example using a container that is evacuated using a vacuum pump. It is known to provide hydrogen gas (at low pressure) in the optical path. The radiation beam is usually a pulsed radiation beam. As each pulse of radiation propagates through the optical path, the gas molecules in the optical path tend to ionize causing a plasma to form in the optical path. The plasma can diffuse away from the optical path so that the plasma extends slightly outside the volume through which the radiation beam propagates.

The first body may be a sensitive object, and therefore it may be necessary to control the flux and/or energy distribution of ions from the plasma incident on the first body. For example, the first body may be a mirror or a sensor in a lithography apparatus or the like.

The second body may comprise one or more walls of the lithography apparatus (which may for example form part of the housing of part of the lithography apparatus such as a mirror or the like). Generally speaking, the second body can be further from the optical path, followed by the first body. It will be appreciated that the second body may comprise a plurality of separate parts (eg, the walls of the lithography apparatus).

It may be necessary to reduce the flux and energy of ions incident on the first body. For example, ions with high energy can pose a risk of sputtering, leading to undesirable degradation of the first body. Additionally, ions (eg, hydrogen ions) can react with components of the first body (such as silicon from glass and stainless steel components and magnesium from aluminum components) to form volatile hydrides. Such volatile hydrogen compounds present within the lithography apparatus may be incident on the surface of the mirror within the lithography apparatus, causing components etched from the first body to be deposited on the mirror surface. Such deposits can absorb EUV radiation, which is undesirable. Furthermore, such deposits can be oxidized and thus can absorb even more EUV radiation. Typically, hydrogen ions do not etch the outer native oxide layer of the material (eg, silicon). However, ions with sufficient kinetic energy can penetrate such oxide layers to the underlying block-like materials, with which the ions can react to form volatile hydrides (eg, silane). Such volatile hydride formation can be stopped if the energy of the hydrogen ions is below the critical kinetic energy such that they cannot penetrate the outer native oxide layer of the material.

To control the flux and energy distribution of ions incident on the first body, one can naively try to apply a bias voltage or potential to the first body. For example, if it is desired to prevent ions from the plasma from impinging on the first body, a positive voltage can be applied to the first body to repel the ions. Similarly, if it is desired to increase the energy or flux of ions from the plasma striking the first body, a negative voltage can be applied to the first body to attract the ions. However, for objects that are close to the plasma, the object is in electrical contact with the plasma (via the plasma sheath). Therefore, simply applying a bias voltage to an object near the plasma will tend to pull the potential of the plasma up to (a small fraction of) the bias potential. The result is that the bias potential does not result in a desired or desired potential difference between the first body and the plasma, and therefore has minimal impact on the flux and energy distribution of ions incident on the first body.

A lithography apparatus according to a first aspect includes two bodies (a first body and a second body), both proximate to an optical path and a voltage supplier configured to apply a potential difference across the first body and the second body. Advantageously, the lithography apparatus according to the first aspect allows a potential difference to be maintained between the first body and the plasma by changing the configuration of the first body and the second body relative to the optical path where the plasma is formed. between. This, in turn, provides some control over the flux and energy distribution of ions incident on the first body.

It should be understood that, as used herein, an object being proximate to an optical path is intended to mean that the object is in the vicinity of the optical path such that the plasma formed in the optical path is connected or connectable to the object.

In some embodiments, the first body and the second body can be configured such that the electrical conductance between the first body and the plasma is significantly less than the electrical conductance between the second body and the plasma, as now described.

The first body and the second body may be configured such that the electrical conductance between the first body and the plasma is significantly less than the electrical conductance between the second body and the plasma.

That is, the resistance between the plasma and the second body is significantly smaller than the resistance between the plasma and the first body. For example, the first body and the second body may be configured such that the electrical conductance between the first body and the plasma is less than half the electrical conductance between the second body and the plasma. For example, the first body and the second body may be configured such that the electrical conductance between the first body and the plasma is less than one-tenth of the electrical conductance between the second body and the plasma.

It will be appreciated that there are several ways in which this conductance difference between the two bodies and the plasma can be achieved. Generally speaking, it is necessary to: (a) reduce the surface area of the first body relative to the second body; (b) increase the density of the plasma between the second body and the optical path; and (c) reduce the distance between the second body and the optical path. The distance between optical paths.

The second body may define a textured surface facing the optical path.

Providing a textured surface on the second body increases the surface area of the second body (compared to a flat surface). Advantageously, this increased surface area increases conductance (reduces resistance) between the plasma and the second body.

The textured surface may be a corrugated surface.

The lithography apparatus may further include a mechanism for creating a conductive medium between the optical path and the second body.

The mechanism for generating a conductive medium between the optical path and the second body may include a voltage supply configured to generate a plasma between the optical path and the second body.

The plasma may be radio frequency (RF) plasma.

Additionally or alternatively, the means for creating a conductive medium between the optical path and the second body may comprise any source of ionizing radiation.

The mechanism for creating a conductive medium between the optical path and the second body may include an electron source configured to increase the density of electrons between the optical path and the second body.

The mechanism for generating a conductive medium between the optical path and the second body may include a radiation source configured to generate radiation that propagates between the optical path and the second body.

This radiation source may include, for example, an ultraviolet (UV) radiation source. Alternatively, the radiation source may comprise an electron beam source, for example.

The second body may include a portion adjacent to the optical path.

For example, the second body may further comprise an additional portion adjacent the optical path, rather than just a wall that forms part of the housing of the lithography apparatus, such as a mirror or the like. This portion may extend from the wall of the lithography apparatus toward the optical path. Advantageously, this can reduce the distance between the plasma generated by the radiation beam and the second body (compared to a configuration that does not have a portion adjacent to the optical path). Advantageously, this reduced distance from the plasma to the second body increases the electrical conductance (reduces resistance) between the plasma and the second body.

The portion adjacent the optical path may extend at least partially around the optical axis of the optical path.

For example, the portion adjacent the optical path may comprise a generally cylindrical or frustoconical hollow body through which the radiation beam propagates.

The voltage supplier can be configured to apply a bias potential to the first body, and the second body can be connected to ground.

For example, to reduce the flux and/or energy of ions from the plasma striking the first body, a positive bias potential may be applied to the first body to repel the ions. Since there can be a significantly greater electrical conductance between the second body and the plasma than there can be between the first body and the plasma, by grounding the second body, the (local) conductance applied to the first body The bias potential may have an insignificant effect on the plasma potential.

Alternatively, the voltage supply may be configured to apply a bias potential to the second body, and the first body may be connected to ground.

For example, to reduce the flux and/or energy from the plasma of ions striking the first body, a negative bias potential can be applied to the second body to attract the ions thereto. As explained above, there may be a significantly greater electrical conductance between the second body and the plasma than there is between the first body and the plasma. Therefore, by applying a negative bias potential to the second body, the potential of the plasma can be significantly reduced. This situation, in turn, reduces the flux and energy of ions impacting the first body (which is grounded).

The second body may be formed from a material that is resistant to etching by plasma.

Advantageously, this can reduce the amount of material that can be etched from the second body (and can subsequently be deposited on sensitive surfaces within the lithography apparatus, such as the surface of a mirror). It should be understood that the first body and the second body may be formed from materials that are compatible with the environment within the EUV lithography apparatus.

The second body may be formed from tungsten.

Tungsten (W) is resistant to etching by hydrogen plasma due to its mass. In addition, tungsten is compatible with the environment within EUV lithography equipment.

In other embodiments, the second body may be formed from another heavy inert metal, such as molybdenum (Mo), ruthenium (Ru), rhodium (Rh), silver (Ag), rhenium (Re), osmium (Os), iridium (Ir) ) or platinum (Pt). Such materials may have at least some resistance to etching by hydrogen plasma.

In some embodiments, the voltage supply may be configured such that the energy of ions incident on the first body is distributed in a manner that causes etching of contaminants on the surface of the first body and does not cause etching of the bulk material of the first body. within the scope as now described.

The voltage supplier may be configured to apply a potential difference across the first body and the second body such that energy from ions incident on the first body is distributed in a manner that causes etching of contaminants on the surface of the first body and causes etching of contaminants on the surface of the first body. Within the minimum etching range of a body of bulk material.

The voltage supply may be configured to apply an AC potential difference across the first body and the second body.

The voltage supply can be configured so that the rate of change of potential across the plasma sheath of the plasma is small most of the time.

Advantageously, the amount of time the potential changes across the plasma sheath is reduced by reducing the amount of time the rate of change of the potential is above a threshold value. In some embodiments, the potential is constant most of the time or changes slowly and oscillates (abruptly) between positive and negative potentials. In some embodiments, the potential oscillates (abruptly) between the positive and negative portions of the duty cycle and is constant or slowly changing in each of the positive and negative portions of the duty cycle.

Advantageously, by reducing the amount of time the potential changes across the plasma sheath, the spread or width of the energy distribution of ions impacting the first component is reduced.

The potential difference may alternate between a positive part, in which the first host system is positively biased, and a negative part, in which the first host system is negatively biased.

The average value of the potential difference applied across the first body and the second body may be non-zero.

The non-zero average value of the potential difference applied across the first body and the second body is the direct current (DC) component of the alternating current potential difference. The average value of the potential difference applied across the first body and the second body depends on the value of the potential difference applied during the positive and negative parts and the duty cycle of the alternating potential difference (i.e., the duration of the negative part and the duration of the positive part The ratio). It will be appreciated that the average energy of the ions impacting the first body depends on the value of the average of the potential differences applied across the first body and the second body.

Although the average energy of the ions impacting the first body is dependent on the value of the average of the potential differences applied across the first body and the second body, the spread or width of the energy distribution of the ions impacting the first component is determined The shape of the periodic potential difference applied across the first body and the second body.

The duty cycle of the potential difference applied across the first body and the second body can be such that the ratio of the duration of the negative portion to the duration of the positive portion is greater than 0.9.

Advantageously, this ensures that the first host system is negatively biased at least 90% of the time in order to attract ions from the plasma and thereby etch contaminants from the first body. The positive portion is the time allowed to remove the charge accumulated on the first body and the second body.

The magnitude of the potential difference applied across the first body and the second body may increase during the negative portion.

For example, the magnitude of the potential difference applied across the first body and the second body may increase linearly during the negative portion. As discussed above, during the negative portion, the first host system is negatively biased in order to attract ions from the plasma to etch contaminants from the first host. During the negative portion, positive surface charge can accumulate on the first body. It should be noted that the first body may be connected to the voltage supply via a matching box or a capacitor. The effect of such surface charges can be accounted for, at least in part, by increasing the magnitude of the potential difference applied across the first body and the second body during the negative portion. Furthermore, this may advantageously reduce the spread or width of the energy distribution of ions impacting the first component.

The frequency of the potential difference applied across the first body and the second body may be less than 400 kHz.

The first body and/or the second body may be connected to the voltage supply via a matching box or capacitor.

By connecting both the first body and the second body to the voltage supply via a matching box or capacitor, the net current averaged over the cycle of the alternating potential difference is zero. Advantageously, since the net current averaged over cycles of AC potential difference is zero, there is no net charge accumulation on the surfaces within lithography apparatus LA for an integer number of cycles of AC potential difference. Thus, it is ensured that there is no net charge accumulation on the surfaces within the lithography apparatus LA due to alternating current potential differences. This accumulation of net charge on the surface within the lithography apparatus LA is undesirable.

The lithography apparatus may include a third body. The third body may be close to the optical path. The third body may be configured to be at ground potential or to be at floating potential. Thus, the third body may not actively control the surface potential.

The lithography apparatus may include a diode electrically connected to the second body. In this way, the surface of the second body is biased relative to ground so as to affect the plasma interaction with the first body. This relative potential can be established by a voltage source or a passive component such as a diode.

The lithography apparatus may be configured to provide the first body at a floating potential, a ground potential, or at another bias potential relative to ground.

According to a second aspect of the present disclosure, a method for controlling the flux and/or energy distribution of ions incident on a first body in a lithography apparatus is provided. The method includes: along an optical path in the lithography apparatus. Directing the radiation beam with a first body proximate the optical path; and applying a potential difference across the first body and a second body also proximate the optical path to control incidence of plasma from the optical path formed in the optical path by the radiation beam. The flux and/or energy distribution of ions on a body.

The lithography equipment may be an extreme ultraviolet (EUV) lithography equipment. In use, the optical path may be maintained at a pressure well below atmospheric pressure, for example using a container that is evacuated using a vacuum pump. It is known to provide hydrogen gas (at low pressure) in the optical path. The radiation beam is usually a pulsed radiation beam. As each pulse of radiation propagates through the optical path, the gas molecules in the optical path tend to ionize causing a plasma to form in the optical path. The plasma can diffuse away from the optical path so that the plasma extends slightly outside the volume through which the radiation beam propagates.

The first body may be a sensitive object, and therefore it may be necessary to control the flux and/or energy distribution of ions from the plasma incident on the first body. For example, the first body may be a mirror or a sensor in a lithography apparatus or the like.

The second body may comprise one or more walls of the lithography apparatus (which may for example form part of the housing of part of the lithography apparatus such as a mirror or the like). Generally speaking, the second body can be further from the optical path, followed by the first body. It will be appreciated that the second body may comprise a plurality of separate parts (eg, the walls of the lithography apparatus).

It may be necessary to reduce the flux and energy of ions incident on the first body. For example, ions with high energy can pose a risk of sputtering, leading to undesirable degradation of the first body. Additionally, ions (eg, hydrogen ions) can react with components of the first body (such as silicon from glass and stainless steel components and magnesium from aluminum components) to form volatile hydrides. Such volatile hydrogen compounds present within the lithography apparatus may be incident on the surface of the mirror within the lithography apparatus, causing components etched from the first body to be deposited on the mirror surface. Such deposits can absorb EUV radiation, which is undesirable. Furthermore, such deposits can be oxidized and thus can absorb even more EUV radiation. Typically, hydrogen ions do not etch the outer native oxide layer of the material (eg, silicon). However, ions with sufficient kinetic energy can penetrate such oxide layers to the underlying block-like materials, with which the ions can react to form volatile hydrides (eg, silane). Such volatile hydride formation can be stopped if the energy of the hydrogen ions is below the critical kinetic energy such that they cannot penetrate the outer native oxide layer of the material.

To control the flux and energy distribution of ions incident on the first body, one can naively try to apply a bias voltage or potential to the first body. For example, if it is desired to prevent ions from the plasma from impinging on the first body, a positive voltage can be applied to the first body to repel the ions. Similarly, if it is desired to increase the energy or flux of ions from the plasma striking the first body, a negative voltage can be applied to the first body to attract the ions. However, for objects that are close to the plasma, the object is in electrical contact with the plasma (via the plasma sheath). Therefore, simply applying a bias voltage to an object near the plasma will tend to pull the potential of the plasma up to the bias potential. The result is that the bias potential does not cause a potential difference between the first body and the plasma, and therefore has minimal impact on the flux and energy distribution of ions incident on the first body.

A method according to a second aspect uses two bodies (a first body and a second body), both close to the optical path and applying a potential difference across the first and second bodies (eg using a voltage supply). Advantageously, the method according to the second aspect allows a potential difference to be maintained between the first body and the plasma by controlling the potential difference applied across the first body and the second body. This, in turn, provides some control over the flux and energy distribution of ions incident on the first body.

It should be understood that, as used herein, an object being proximate to an optical path is intended to mean that the object is in the vicinity of the optical path such that the plasma formed in the optical path is connected or connectable to the object.

In some embodiments, the first body and the second body can be configured such that the electrical conductance between the first body and the plasma is significantly less than the electrical conductance between the second body and the plasma, as now described.

The first body and the second body may be configured such that the electrical conductance between the first body and the plasma is significantly less than the electrical conductance between the second body and the plasma.

That is, the resistance between the plasma and the second body is significantly smaller than the resistance between the plasma and the first body. For example, the first body and the second body may be configured such that the electrical conductance between the first body and the plasma is less than half the electrical conductance between the second body and the plasma. For example, the first body and the second body may be configured such that the electrical conductance between the first body and the plasma is less than one-tenth of the electrical conductance between the second body and the plasma.

It will be appreciated that there are several ways in which this conductance difference between the two bodies and the plasma can be achieved. Generally speaking, it is necessary to: (a) reduce the surface area of the first body relative to the second body; (b) increase the density of the plasma between the second body and the optical path; and (c) reduce the distance between the second body and the optical path. The distance between optical paths.

The method may further include creating a conductive medium between the optical path and the second body.

Generating the conductive medium between the optical path and the second body may include generating a plasma between the optical path and the second body.

The plasma may be radio frequency (RF) plasma.

Additionally or alternatively, the means for generating a conductive medium may include any source of ionizing radiation.

Creating a conductive medium between the optical path and the second body may include increasing a density of electrons between the optical path and the second body.

Producing a conductive medium between the optical path and the second body may include directing radiation to propagate between the optical path and the second body.

This radiation may include, for example, ultraviolet (UV) radiation. Alternatively, the radiation may comprise an electron beam source, for example.

Applying a potential difference across the first body and the second body may include applying a bias potential to the first body and grounding the second body.

For example, to reduce the flux and/or energy of ions from the plasma impinging on the first body, a positive bias potential may be applied to the first body to repel the plasma. Since there can be a significantly greater conductance between the second body and the plasma than there is between the first body and the plasma, by grounding the second body, the (local) conductance applied to the first body ) The bias potential may have an insignificant effect on the plasma potential.

Applying a potential difference across the first body and the second body may include applying a bias potential to the second body and grounding the first body.

For example, to reduce the flux and/or energy from the plasma of ions striking the first body, a negative bias potential can be applied to the second body to attract the ions thereto. As explained above, there may be a significantly greater electrical conductance between the second body and the plasma than there is between the first body and the plasma. Therefore, by applying a negative bias potential to the second body, the potential of the plasma can be significantly reduced. This situation, in turn, reduces the flux and energy of ions impacting the first body (which is grounded).

The second body may be formed from a material that is resistant to etching by plasma.

Advantageously, this can reduce the amount of material that can be etched from the second body (and can subsequently be deposited on sensitive surfaces within the lithography apparatus, such as the surface of a mirror). It should be understood that the first body and the second body may be formed from materials that are compatible with the environment within the EUV lithography apparatus.

The second body may be formed from tungsten.

Tungsten (W) is resistant to etching by hydrogen plasma due to its mass. In addition, tungsten is compatible with the environment within EUV lithography equipment.

In other embodiments, the second body may be formed from another heavy inert metal, such as molybdenum (Mo), ruthenium (Ru), rhodium (Rh), silver (Ag), rhenium (Re), osmium (Os), iridium (Ir) ) or platinum (Pt). Such materials may have at least some resistance to etching by hydrogen plasma.

In some embodiments, the applied voltage can be such that the energy of the ions incident on the first body is distributed in a range that causes etching of contaminants on the surface of the first body and does not cause etching of the bulk material of the first body. Inside, as now described.

Applying a potential difference across the first body and the second body can cause the energy from the ions of the plasma incident on the first body to be distributed in a manner that results in etching of contaminants on the surface of the first body and results in the bulk material of the first body. Within the scope of minimum etching.

Applying a potential difference across the first body and the second body may include applying an AC potential difference across the first body and the second body.

Applying a potential difference across the first body and the second body can cause the rate of change of potential across the plasma sheath of the plasma to be small most of the time.

Advantageously, the amount of time the potential changes across the plasma sheath is reduced by reducing the amount of time the rate of change of the potential is above a threshold value. In some embodiments, the potential is constant most of the time or changes slowly and oscillates (abruptly) between positive and negative potentials. In some embodiments, the potential oscillates (abruptly) between the positive and negative portions of the duty cycle and is constant or slowly changing in each of the positive and negative portions of the duty cycle.

Advantageously, by reducing the amount of time the potential changes across the plasma sheath, the spread or width of the energy distribution of ions impacting the first component is reduced.

The potential difference may alternate between a positive portion, in which the first host system is positively biased, and a negative potential, in which the first host system is negatively biased.

The average value of the potential difference applied across the first body and the second body may be non-zero.

The non-zero average value of the potential difference applied across the first body and the second body is the direct current (DC) component of the alternating current potential difference. The average value of the potential difference applied across the first body and the second body depends on the value of the potential difference applied during the positive and negative parts and the duty cycle of the alternating potential difference (i.e., the duration of the negative part and the duration of the positive part The ratio). It will be appreciated that the average energy of the ions impacting the first body depends on the value of the average of the potential differences applied across the first body and the second body.

Although the average energy of the ions impacting the first body is dependent on the value of the average of the potential differences applied across the first body and the second body, the spread or width of the energy distribution of the ions impacting the first component is determined The shape of the periodic potential difference applied across the first body and the second body.

The duty cycle of the potential difference applied across the first body and the second body can be such that the ratio of the duration of the negative portion to the duration of the positive portion is greater than 0.9.

Advantageously, this ensures that the first host system is negatively biased at least 90% of the time in order to attract ions from the plasma and thereby etch contaminants from the first body. The positive portion is the time allowed to remove the charge accumulated on the first body and the second body.

The magnitude of the potential difference applied across the first body and the second body may increase during the negative portion.

For example, the magnitude of the potential difference applied across the first body and the second body may increase linearly during the negative portion. As discussed above, during the negative portion, the first host system is negatively biased in order to attract ions from the plasma to etch contaminants from the first host. During the negative portion, positive surface charge can accumulate on the first body. It should be noted that the first body may be connected to the voltage supply via a matching box or a capacitor. The effect of such surface charges can be accounted for, at least in part, by increasing the magnitude of the potential difference applied across the first body and the second body during the negative portion. Furthermore, this may advantageously reduce the spread or width of the energy distribution of ions impacting the first component.

The frequency of the potential difference applied across the first body and the second body may be less than 400 kHz.

The first body and/or the second body may be connected to the voltage supply via a matching box or capacitor.

By connecting both the first body and the second body to the voltage supply via a matching box or capacitor, the net current averaged over the cycle of the alternating potential difference is zero. Advantageously, since the net current averaged over cycles of AC potential difference is zero, there is no net charge accumulation on the surfaces within lithography apparatus LA for an integer number of cycles of AC potential difference. Thus, it is ensured that there is no net charge accumulation on the surfaces within the lithography apparatus LA due to alternating current potential differences. This accumulation of net charge on the surface within the lithography apparatus LA is undesirable.

The method may further include providing the third body at ground potential or at floating potential. In other words, there is no active control of the surface potential.

The method may further include providing a diode in electrical connection with the second body thereby biasing the second body relative to ground.

The method may further include providing the first body at a floating potential, a ground potential, or at another bias potential relative to ground.

It will be understood that one or more aspects or features described above or referenced in the following description may be combined with one or more other aspects or features.

Figure 1 shows the lithography system. The lithography system includes a radiation source SO and a lithography equipment LA. Radiation source SO is configured to generate beam B of extreme ultraviolet (EUV) radiation. Lithography apparatus LA includes an illumination system IL, a support structure MT configured to support a reticle assembly 15 including a patterning device MA (eg, a reticle or mask), a projection system PS, and a reticle configured to The substrate table WT is used to support the substrate W. Illumination system IL is configured to condition radiation beam B prior to its incidence on patterning device MA. The projection system is configured to project radiation beam B (now patterned by patterning device MA) onto substrate W. The substrate W may include previously formed patterns. In this case, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W.

The radiation source SO, the lighting system IL and the projection system PS may all be constructed and configured such that they are isolated from the external environment. A gas with a pressure below atmospheric pressure (eg, hydrogen) may be provided in the radiation source SO. The vacuum can be provided in the lighting system IL and/or the projection system PS. A small amount of gas (eg, hydrogen) with a pressure well below atmospheric pressure may be provided in the lighting system IL and/or the projection system PS.

The radiation source SO shown in Figure 1 is of a type that may be called a laser produced plasma (LPP) source. The laser 1 , which may be, for example, a CO2 laser, is configured to deposit energy via the laser beam 2 into a fuel, such as tin (Sn), provided from a fuel emitter 3 . Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form, and may be, for example, a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, for example in the form of droplets, along a trajectory towards the plasma formation zone 4 . The laser beam 2 is incident on the tin at the plasma formation zone 4. Deposition of laser energy into the tin generates a plasma 7 at the plasma formation zone 4 . Radiation, including EUV radiation, is emitted from the plasma 7 during the deexcitation and recombination of the ions of the plasma.

EUV radiation is collected and focused by a near normal incidence radiation collector 5 (sometimes more commonly referred to as a normal incidence radiation collector). Collector 5 may have a multilayer structure configured to reflect EUV radiation (eg, EUV radiation having a desired wavelength, such as 13.5 nm). The collector 5 may have an elliptical configuration with two elliptical foci. The first focus point may be at the plasma formation zone 4 and the second focus point may be at the intermediate focus point 6, as discussed below.

In other embodiments of laser produced plasma (LPP) sources, the collector 5 may be a so-called grazing incidence collector configured to receive EUV radiation at a grazing incidence angle and focus the EUV radiation at an intermediate focus. For example, the grazing incidence collector may be a nested collector, which includes a plurality of grazing incidence reflectors. The grazing incidence reflector may be positioned axially symmetrically about the optical axis.

The radiation source SO may include one or more contaminant traps (not shown). For example, a contaminant trap may be located between the plasma formation zone 4 and the radiation collector 5 . The contaminant trap may be, for example, a rotating foil trap, or may be any other suitable form of contaminant trap.

The laser 1 is separable from the radiation source SO. In this case, the laser beam 2 can be delivered from the laser 1 to the radiation by means of a beam delivery system (not shown) including, for example, suitable guide mirrors and/or beam expanders and/or other optical components. SourceSO. Laser 1 and radiation source SO can together be considered a radiation system.

The radiation reflected by collector 5 forms radiation beam B. The radiation beam B is focused at point 6 to form an image of the plasma formation zone 4, which image acts as a virtual radiation source for the illumination system IL. The point 6 at which the radiation beam B is focused may be called the intermediate focus. The radiation source SO is configured such that the intermediate focus 6 is located at or near the opening 8 in the enclosure 9 of the radiation source SO.

The radiation beam B is passed from the radiation source SO into the lighting system IL, which is configured to regulate the radiation beam. The illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11 . The faceted field mirror device 10 and the faceted pupil mirror device 11 together provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B is transmitted from the illumination system IL and is incident on the reticle assembly 15 held by the support structure MT. The reticle assembly 15 includes a patterning device MA and a surface film 19 . The pellicle is mounted to the patterning device MA via the pellicle frame 17 . The reticle assembly 15 may be called a reticle and film assembly 15 . Patterning device MA reflects and patterns radiation beam B. In addition to or instead of the faceted field mirror device 10 and the faceted pupil mirror device 11 , the illumination system IL may also include other mirrors or devices. Although this exemplary embodiment shows the pellicle 19 (as part of the reticle assembly 15), in some other embodiments, no pellicle may be present, in which case the patterning device MA is supported by the support structure MT .

After reflection from the patterning device MA, the patterned radiation beam B enters the projection system PS. The projection system includes a plurality of mirrors 13, 14 configured to project a radiation beam B onto a substrate W held by a substrate table WT. The projection system PS can apply a reduction factor to the radiation beam, thereby forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 may be applied. Although in Figure 1 the projection system PS has two mirrors 13, 14, the projection system PS may include any number of mirrors (eg, six mirrors).

The lithography apparatus may, for example, be used in a scanning mode, in which the support structure (e.g., mask table) MT and the substrate table WT are simultaneously scanned while projecting the pattern imparted to the radiation beam onto the substrate W (i.e., dynamic exposure ). The speed and direction of the substrate table WT relative to the support structure (eg, mask table) MT can be determined by the reduction ratio and image reversal characteristics of the projection system PS. The patterned radiation beam incident on the substrate W may include radiation strips. The radiation band may be referred to as the exposure gap. During scanning exposure, movement of the substrate table WT and support structure MT may cause the exposure slit to travel throughout the exposure field of the substrate W.

The radiation source SO and/or the lithography apparatus shown in FIG. 1 may include components not shown. For example, a spectral filter may be provided in the radiation source SO. Spectral filters can substantially transmit EUV radiation but substantially block radiation of other wavelengths, such as infrared radiation.

In other embodiments of the lithography system, the radiation source SO may take other forms. For example, in alternative embodiments, the radiation source SO may include one or more free electron lasers. The one or more free electron lasers can be configured to emit EUV radiation that can be provided to one or more lithography equipment.

As briefly described above, the reticle assembly 15 includes a pellicle 19 provided adjacent the patterning device MA. The surface film 19 is provided in the path of the radiation beam B such that the radiation beam B passes through the surface both when it approaches the patterning device MA from the illumination system IL and when it reflects from the patterning device MA towards the projection system PS. Membrane 19. The membrane 19 includes a film or membrane that is substantially transparent to EUV radiation (although it will absorb a small amount of EUV radiation). As used herein, EUV transparent film or film substantially transparent to EUV radiation means that the film 19 transmits at least 65% of EUV radiation, preferably at least 80% and more preferably at least 90% of EUV radiation. The film 19 is used to protect the patterning device MA from particle contamination.

Despite efforts to maintain a clean environment inside the lithography equipment LA, particles may still exist inside the lithography equipment LA. In the absence of pellicle 19, particles may be deposited onto the patterning device MA. Particles on the patterning device MA may adversely affect the pattern imparted to the radiation beam B and thus the pattern transferred to the substrate W. The membrane 19 advantageously provides a barrier between the patterning device MA and the environment in the lithography apparatus LA to prevent particles from depositing on the patterning device MA.

The pellicle 19 is positioned at a distance from the patterning device MA that is sufficient so that any particles incident on the surface of the pellicle 19 are not in the field plane of the lithography apparatus LA. This spacing between the film 19 and the patterning device MA serves to reduce the extent to which any particles on the surface of the film 19 impart a pattern to the radiation beam B imaged onto the substrate W. It will be appreciated that in the case where a particle is present in the radiation beam B but at a location that is not in the field plane of the radiation beam B (eg, not at the surface of the patterning device MA), then any image of the particle will not be focused on on the surface of the substrate W. In the absence of other considerations, it may be necessary to position the membrane 19 a substantial distance from the patterning device MA. However, in practice, the space available for accommodating the pellicle in the lithography apparatus LA is limited due to the presence of other components. In some embodiments, the spacing between the pellicle 19 and the patterning device MA may, for example, be approximately between 1 mm and 10 mm, such as between 1 mm and 5 mm, such as between 2 mm and 2.5 mm.

The lithography apparatus LA shown in Figure 1 includes a plurality of optical elements 10, 11, 13, 14 (shown schematically in Figure 1) defining optical paths. The optical elements 10, 11, 13, 14 are configured to receive the radiation beam B from the radiation source SO, project the radiation beam B onto the reticle MA to pattern the radiation beam B and form the reticle MA on the substrate W image.

In use, the optical path of the lithography apparatus LA may be maintained at a pressure well below atmospheric pressure, for example using a container that is evacuated using a vacuum pump. It is known to provide hydrogen gas (at low pressure) in the optical path. Radiation beam B is usually a pulsed radiation beam. As each pulse of radiation propagates through the optical path, the gas molecules in the optical path tend to ionize causing a plasma to form in the optical path. The plasma may diffuse away from the optical path such that the plasma extends slightly outside the volume through which the radiation beam B propagates.

It may be necessary to reduce the flux and energy of ions incident on some components within the lithography apparatus LA. For example, ions with high energy can pose a risk of sputtering, leading to undesirable degradation of the bulk of these components. Additionally, ions (eg, hydrogen ions) can react with components of the bulk of the component (such as silicon from glass and stainless steel components and magnesium from aluminum components) to form volatile hydrides. Such volatile hydrogen compounds present in the lithography apparatus LA may be incident on the surfaces of the mirrors 10, 11, 13, 14 in the lithography apparatus LA, thereby causing components etched from some components to be deposited on the mirrors 10, 11 , 13, 14 on. Such deposits can absorb EUV radiation, which is undesirable. Furthermore, such deposits can be oxidized and thus can absorb even more EUV radiation. Typically, hydrogen ions do not etch the outer native oxide layer of the material (eg, silicon Si). However, ions with sufficient kinetic energy can penetrate such oxide layers to the underlying block-like materials, with which the ions can react to form volatile hydrides (eg, silane _SiH4 ). Such volatile hydride formation can be stopped if the energy of the hydrogen ions is below the critical kinetic energy such that they cannot penetrate the outer native oxide layer of the material.

It may be necessary to provide ions near certain components within the lithography apparatus LA, or to direct the ions so as to be incident on such components. For example, the ions may react with contaminants that prevent their deposition on the surfaces of the mirrors 10, 11, 13, 14 within the lithography apparatus LA. Similarly, ions incident on the surfaces of mirrors 10 , 11 , 13 , 14 within lithography apparatus LA may etch such contaminants from mirrors 10 , 11 , 13 , 14 .

To control the flux and energy distribution of ions incident on a body, one can naively try to apply a bias voltage or potential to the body. For example, if it is desired to prevent ions from the plasma from impinging on the body, a positive voltage can be applied to the first body to repel the ions. Similarly, if it is desired to increase the energy or flux of ions from the plasma striking the first body, a negative voltage can be applied to the first body to attract the ions. However, the inventors have realized that for an object to be in close proximity to the plasma, the object is in electrical contact with the plasma (via the plasma sheath). Therefore, simply applying a bias voltage to an object near the plasma will tend to pull the potential of the plasma up to (a small fraction of) the bias potential. The result is that the bias potential does not result in a desired or desired potential difference between the biased body and the plasma, and therefore has minimal impact on the flux and energy distribution of ions incident on the first body.

According to an embodiment of the present disclosure, a lithography apparatus LA of the type shown in Figure 1 is provided, comprising a plurality of optical elements 10, 11, 13, 14 defining an optical path. The optical elements 10, 11, 13, 14 are configured to receive the radiation beam B from the radiation source SO, project the radiation beam B onto the reticle MA to pattern the radiation beam B and form the reticle MA on the substrate W image. A lithography apparatus LA according to an embodiment of the present disclosure includes two bodies proximate the optical path and a voltage supply, as now discussed with reference to FIG. 2 .

In Figure 2, a plasma 100 formed in a lithography apparatus LA when a radiation beam B propagates along an optical path is schematically shown. Lithography apparatus LA includes a first body 102 and a second body 104 . Within the lithography apparatus LA, both the first body 102 and the second body 104 are close to the optical path and thus to the plasma 100 . It should be understood that as used herein, an object being proximate to an optical path is intended to mean that the object is in the vicinity of the optical path such that the plasma 100 formed in the optical path is connected or connectable to the object. As will be appreciated by those skilled in the art, the main body of plasma 100 is surrounded by a plasma sheath 106 that extends to surrounding objects including first body 102 and second body 104 .

Lithography apparatus LA further includes a voltage supplier 108 configured to apply a potential difference across the first body 102 and the second body 104 . In the example shown, voltage supplier 108 is configured to apply bias potential V _b to first body 102 and second body 104 is grounded. It should be appreciated that in alternative embodiments, voltage supply 108 may be configured to apply bias potential V _b to second body 104 and first body 102 may be grounded. Generally speaking, the voltage supply 108 is configured to maintain the first body 102 and the second body 104 at different potentials such that a potential difference exists across the first body 102 and the second body 104 .

Particularly for embodiments in which voltage supply 108 is configured to apply an AC potential difference across first body 102 and second body 104 , each of first body 102 and second body 104 may be connected to the bias via a matching box or capacitor 110 Potential.

The first body 102 , the second body 104 and/or the voltage supply 108 are configured to control the flux of ions incident on the first body 102 from the plasma 100 formed in the optical path by the radiation beam B and/or or energy distribution.

For example, to reduce the flux and/or energy of ions from the plasma 100 that impinge on the first body 102, a forward bias potential V _b may be applied to the first body 102 to repel the ions. Since there can be significantly greater electrical conductance between the second body 104 and the plasma 100 than there can be between the first body 102 and the plasma 100 , by grounding the second body 104 , applying to the first The (local) bias potential of the body 102 may have an insignificant effect on the plasma potential.

Alternatively, in other embodiments, to reduce the flux and/or energy of ions from the plasma 100 that impinge on the first body 102 , a negative bias potential may be applied to the second body 104 to attract the ions. onto it. As explained below, there may be a significantly greater electrical conductance between the second body 104 and the plasma 100 than there is between the first body 102 and the plasma 100 . Therefore, by applying a negative bias potential to the second body 104, the potential of the plasma can be significantly reduced. This, in turn, reduces the flux and energy of ions impacting the first body 102 (which is grounded).

The first body 102 may be a sensitive object, and therefore it may be necessary to control the flux and/or energy distribution of ions from the plasma 100 incident on the first body 102 . For example, the first body 102 may be a mirror or a sensor in a lithography apparatus, or the like. Alternatively, the first body 102 may be any object within a lithography apparatus (eg, formed of glass, stainless steel, or aluminum) upon which ions with sufficient energy to penetrate the bulk material are incident. Volatile hydrogen compounds are released from these items.

The second body 104 may comprise one or more walls of the lithography apparatus LA (which may, for example, form part of the housing of the lithography apparatus LA, such as a mirror or the like). Generally speaking, the second body 104 may be further from the optical path, followed by the first body 102 . It will be appreciated that the second body 104 may comprise a plurality of separate parts (eg, the wall of the lithography apparatus LA).

Lithography apparatus LA according to the present disclosure includes two bodies (a first body 102 and a second body 104 ), both close to the optical path (and thus, in use, the plasma 100 ) and a voltage supplier 108 Configured to apply a potential difference across the first body 102 and the second body 104 . Advantageously, the lithography apparatus LA according to the present disclosure allows the potential difference to be maintained in the first body 102 by changing the configuration of the first body 102 and the second body 104 relative to the optical path where the plasma 100 is formed. Between 100 and Plasma. This, in turn, provides some control over the flux and energy distribution of ions incident on the first body 102 .

In some embodiments, first body 102 and second body 104 are configured such that the electrical conductance between first body 102 and plasma 100 is significantly less than the electrical conductance between second body 104 and plasma 100, as now described. A simplified electrostatic model is depicted in Figure 2, where the first body 102 is connected to the plasma 100 via the plasma sheath 106, schematically shown with a first resistance _R1 , and the second body 104 is connected to the plasma via the plasma sheath 106. Slurry 100 is schematically shown having a second resistance _R2 . It is proposed that the first body 102 and the second body 104 should be configured such that R ₂ << R ₁ .

That is, the resistance R ₂ between the plasma 100 and the second body 104 is significantly smaller than the resistance R ₁ between the plasma 100 and the first body 102 . For example, first body 102 and second body 104 may be configured such that the electrical conductance between first body 102 and plasma 100 is less than half the electrical conductance between second body 104 and plasma 100 . For example, first body 102 and second body 104 may be configured such that the electrical conductance between first body 102 and plasma 100 is less than one-tenth of the electrical conductance between second body 104 and plasma 100 .

It should be noted that this configuration, in which the resistance R ₂ between the plasma 100 and the second body 104 is significantly smaller than the resistance R ₁ between the plasma 100 and the first body 102 , is not typical of known lithography apparatuses. For example, generally speaking, the first body 102 may be a sensitive object, and the flux and/or energy distribution of ions received by the sensitive object need to be controlled. Such a body 102 may generally be in close proximity to the plasma 100, and thus the resistance _R1 may be relatively low. For this reason, biasing the first body 102 alone will generally not have a significant effect on the flux and energy distribution of ions (since this lower resistance _R1 will mean that the plasma potential can be greatly affected by the bias potential ). The second body 104 may comprise one or more walls of the lithography apparatus LA (which may, for example, form part of the housing of the lithography apparatus LA, such as a mirror or the like). Such a body 104 may generally be significantly further away from the plasma 100 than the first body 102, and thus the resistance _R2 may be relatively high. In at least some embodiments of the present disclosure, the lithography apparatus LA has been modified in some manner to ensure that the resistance R ₂ between the plasma 100 and the second body 104 is significantly less than that between the plasma 100 and the first body 102 resistor R ₁ .

It should be appreciated that there are several ways in which this difference in conductance between the first and second bodies 102 and 104 and the plasma 100 (ie, the condition of R ₂ << R ₁ ) can be achieved. Generally speaking, it is desirable to: (a) reduce the surface area of first body 102 relative to second body 104; (b) increase the density of plasma 100 between second body 104 and the optical path; and (c) reduce The distance between the second body 104 and the optical path is small.

In some embodiments, the second body 104 may define a textured surface facing the optical path. Providing a textured surface on the second body 104 increases the surface area of the second body 104 (compared to a flat surface). Advantageously, this increased surface area increases the conductance between plasma 100 and second body 104 (reduces resistance _R2 ). For example, the textured surface of the second body 104 may be a corrugated surface.

In some embodiments, the lithography apparatus LA may further include a mechanism 112 for creating a conductive medium between the optical path and the second body 104 .

The mechanism 112 for generating a conductive medium between the optical path and the second body 104 may include a voltage supply configured to generate a plasma between the optical path and the second body 104 . The plasma may be a radio frequency (RF) plasma.

Additionally or alternatively, the mechanism 112 for creating a conductive medium between the optical path and the second body 104 may include any source of ionizing radiation 114 (shown schematically in Figure 2).

For example, the mechanism 112 for creating a conductive medium between the optical path and the second body 104 may include an electron source configured to increase electron density between the optical path and the second body 102 .

In some embodiments, the mechanism 112 for creating a conductive medium between the optical path and the second body 104 may include a radiation source configured to generate a radiation propagating between the optical path and the second body 104 . radiation. The radiation source may include, for example, an ultraviolet (UV) radiation source. Alternatively, the radiation source may comprise, for example, an electron beam source.

In some embodiments, the second body 104 may include a portion adjacent the optical path. For example, the second body 104 may further comprise an additional portion adjacent the optical path, rather than just a wall that forms part of the housing of the lithography apparatus LA, such as a mirror or the like. This portion may extend from the wall of the lithography apparatus toward the optical path. Advantageously, this may reduce the distance between the plasma 100 produced by the radiation beam and the second body 104 (compared to a configuration that does not have a portion adjacent to the optical path). Advantageously, this reduces the distance from the plasma 100 to the second body 104 and increases the conductance between the plasma 100 and the second body 104 (reduces the resistance _R2 ).

In some embodiments, the portion of the second body 104 adjacent the optical path extends at least partially around the optical axis of the optical path. For example, the portion of the second body 104 adjacent the optical path may comprise a generally cylindrical or frustoconical hollow body through which the radiation beam B propagates.

In some embodiments, second body 104 may be formed from a material that is resistant to etching by plasma 100 . Advantageously, this can reduce the amount of material that can be etched from the second body 104 (and can subsequently be deposited on sensitive surfaces (such as mirrored surfaces) within the lithography apparatus LA). It should be appreciated that the first body 102 and the second body 104 may be formed from materials that are compatible with the environment within the EUV lithography apparatus LA.

In some embodiments, second body 104 may be formed from tungsten. Tungsten (W) is resistant to etching by hydrogen plasma 100 due to its mass. In addition, tungsten is compatible with the environment within EUV lithography equipment LA.

In other embodiments, the second body may be formed from another heavy inert metal, such as molybdenum (Mo), ruthenium (Ru), rhodium (Rh), silver (Ag), rhenium (Re), osmium (Os), iridium (Ir) ) or platinum (Pt). Such materials may have at least some resistance to etching by hydrogen plasma.

In some embodiments, the voltage supply 108 is configured such that the energy of the ions incident on the first body 102 is distributed in a manner that causes etching of contaminants on the surface of the first body 102 and does not cause blockage of the first body 102 The materials are etched within the scope as now described.

Voltage supplier 108 may be configured to apply a potential difference V _b across first body 102 and second body 104 such that the energy distribution of ions from plasma 100 incident on first body 102 results in a surface of first body 102 The etching of contaminants on the first body 102 results in minimal etching of the bulk material of the first body 102 . An exemplary potential difference V _b used to achieve this is now described with reference to FIG. 3 .

In some embodiments, the voltage supply 108 is configured such that a potential difference V _b is applied across the first body 102 and the second body 104 having a waveform 200 as shown in FIG. 3 .

The potential difference V _b shown in FIG. 3 is an AC potential difference V _b with a specific waveform 200 .

When a potential difference V _b is applied having the waveform 200 shown in FIG. 3 , the rate of change of the potential across the plasma sheath 106 of the plasma 100 is small most of the time. Advantageously, by reducing the amount of time the rate of change of potential V _b is above a threshold value, the amount of time the potential changes across the plasma sheath 106 is reduced. In the embodiment shown in Figure 3, the potential _Vb is constant most of the time or varies slowly and oscillates (suddenly) between positive and negative potentials. In the embodiment shown in Figure 3, the potential _Vb oscillates (suddenly) between the positive portion 202 and the negative portion 204 of the duty cycle, and in each of the positive portion 202 and the negative portion 204 of the duty cycle Among them, the potential V _b is constant or changes slowly.

Advantageously, by reducing the amount of time the potential changes across the plasma sheath 106, the spread or width of the energy distribution of ions impacting the first component 102 is reduced. This bias potential V _b thus allows accurate control of the energy of the ions impacting the first component 102 .

In the embodiment shown in Figure 3, the potential difference _Vb alternates between a positive portion 202, in which the first body 102 is positively biased, and a negative portion 204, in which the first body 102 is negatively biased.

When a potential difference V _b is applied having the waveform 200 shown in FIG. 3 , the average value of the potential difference <V _b > applied across the first body 102 and the second body 104 is non-zero. The non-zero average value of the potential difference <V _b > applied across the first body 102 and the second body 104 is the direct current (DC) component of the alternating current potential difference V _b . The average value of the potential difference <V _b > applied across the first body 102 and the second body 104 depends on the value of the potential difference applied during the positive portion 202 and the negative portion 204 and the duty cycle of the AC potential difference (i.e., the negative portion 204 The ratio of the duration to the duration of the positive part 202). It should be understood that the average energy of the ions impacting the first body 102 depends on the value of the average value of the potential difference <V _b > applied across the first body 102 and the second body 104 .

Although the average energy of the ions impacting the first body 102 depends on the value of the average of the potential differences <V _b > applied across the first body 102 and the second body 104 , the energy of the ions impacting the first component 102 The spread or width of the energy distribution depends on the shape of the periodic potential difference V _b applied across the first body 102 and the second body 104 .

If a sinusoidal potential difference is applied across the first body 102 and the second body 104, the potential across the plasma sheath 106 continues to change. Therefore, there is a broad distribution of ion energies of ions incident on the first body 102 . Therefore, it may be impossible to ensure that all ions incident on the first body 102 have energies that are both: (a) above the threshold for etching contaminants; and (b) below the threshold for etching contaminants. The threshold value of the bulk material of the first body 102 . In contrast, when a potential difference V _b having the waveform 200 shown in FIG. 3 is applied across the first body 102 and the second body 104 , the potential across the plasma sheath 106 is generally constant. This situation results in an extremely narrow distribution of ion energy for ions incident on the first body 102 . Additionally, a stable potential across the plasma sheath 106 results in low electron heating. Therefore, when a potential difference V _b having the waveform 200 shown in FIG. 3 is applied across the first body 102 and the second body 104 , advantageously, it is possible to ensure that all ions incident on the first body 102 have both The energy is: (a) above the threshold for etching contaminants; and (b) below the threshold for etching the bulk material of first body 102 .

In some embodiments, the duty cycle of the potential difference V _b applied across the first body 102 and the second body 104 is such that the ratio of the duration of the negative portion 204 to the duration of the positive portion 202 is greater than 0.9. Advantageously, this ensures that the first body 102 is negatively biased at least 90% of the time in order to attract ions from the plasma 100 and thereby etch contaminants from the first body 102 . The positive portion 202 allows time to remove the charge accumulated on the first body 102 and the second body 104 .

In the embodiment shown in FIG. 3 , the magnitude of the potential difference |V _b | applied across the first body 102 and the second body 104 increases during the negative portion 204 . For example, in this embodiment, the magnitude of the potential difference |V _b | applied across the first body 102 and the second body 104 increases linearly during the negative portion 204 . As discussed above, during negative portion 204 , first body 102 is negatively biased in order to attract ions from plasma 100 to etch contaminants from first body 102 . During the negative portion, positive surface charges may accumulate on the first body 102 . It should be noted that the first body 102 may be connected to the voltage supply 108 via a matching box or capacitor 110 . The effect of such surface charges can be accounted for, at least in part, by increasing the magnitude of the potential difference V _b applied across the first body 102 and the second body 104 during the negative portion 204 . Additionally, this can advantageously reduce the spread or width of the energy distribution of ions impacting the first component 102 .

In some embodiments, the frequency of the potential difference V _b applied across the first body 102 and the second body 104 is less than 400 kHz.

In embodiments in which the bias voltage V _b shown in FIG. 3 is applied to the first body 102 (or the second body 104 ), the first body 102 and/or the second body 104 may be connected via a matching box or capacitor 110 to voltage supplier 108. By connecting both the first body 102 and the second body 104 to the voltage supply 108 via a matching box or capacitor 110, the net current averaged over the cycle of the AC potential difference is zero. Advantageously, since the net current averaged over cycles of AC potential difference is zero, there is no net charge accumulation on the surfaces within lithography apparatus LA for an integer number of cycles of AC potential difference. Thus, it is ensured that there is no net charge accumulation on the surfaces within the lithography apparatus LA due to alternating current potential differences. This accumulation of net charge on the surface within the lithography apparatus LA is undesirable.

According to some embodiments of the present disclosure, a method of controlling the flux and/or energy distribution of ions incident on the first body 102 within the lithography apparatus LA is provided. As shown in Figure 4, the method 300 includes the step 302 of directing the radiation beam B along an optical path in the lithography apparatus LA to which the first body 102 is proximate. The method 300 further includes step 304 of applying a potential difference across the first body 102 and the second body 104 also proximate the optical path to control incidence on the first body 102 from the plasma 100 formed in the optical path by the radiation beam B The flux and/or energy distribution of ions on the

It will be appreciated that method 300 may include any or all of the features of lithography apparatus LA as described above with reference to Figures 1-3.

The method 300 uses two bodies (a first body 102 and a second body 104) that are both proximate to the optical path and apply a potential difference across the first body 102 and the second body 104 (eg, using a voltage supply). Advantageously, by controlling the potential difference applied across the first body 102 and the second body 104, the method 300 allows the potential difference to be maintained between the first body 102 and the plasma 100. This, in turn, provides some control over the flux and energy distribution of ions incident on the first body 102 .

It will be understood that as used herein, the flux of ions incident on a body is intended to mean the number of ions incident on the body per unit area per unit time.

According to the embodiment depicted in Figure 5, a plasma 100 formed in a lithography apparatus LA as a radiation beam B propagates along an optical path is schematically shown. Lithography apparatus LA includes a first body 102 and a second body 104 as well as a third body 116 . Within the lithography apparatus LA, the first body 102 , the second body 104 and the third body 116 are each close to the optical path and therefore to the plasma 100 . It should be understood that as used herein, an object close to an optical path is intended to mean that the object is near the optical path such that the plasma 100 formed in the optical path is connected or connectable to the object. As those skilled in the art will appreciate, the main system of plasma 100 is surrounded by a plasma sheath 106 that extends to surrounding objects including first body 102 , second body 104 , and third body 116 .

In the depicted embodiment, the third body 116 is grounded, but the third body may alternatively be allowed to have a floating potential. Thus, there is no active control of the surface potential of the third body 116. The second body 104 is electrically biased relative to ground to affect plasma interactions with the first body 102, which may be an optical element such as a mirror. The potential relative to ground may be provided as a voltage source 108 or via a passive component such as a diode. The first body 102 includes important surfaces where plasma interactions need to be controlled and this is accomplished by biasing the second body 104 . The first body 102 may be at a floating potential, connected to ground potential, or at another bias potential relative to ground. Voltage source 108 may be configured to operate as described herein.

The first body 102 may be a sensitive object, and therefore it may be necessary to control the flux and/or energy distribution of ions from the plasma 100 incident on the first body 102 . For example, the first body 102 may be a mirror or a sensor in a lithography apparatus, or the like. Alternatively, the first body 102 may be any object within a lithography apparatus (eg, formed of glass, stainless steel, or aluminum) upon which ions with sufficient energy to penetrate the bulk material are incident. Volatile hydrogen compounds are released from these items.

The second body 104 may comprise one or more walls of the lithography apparatus LA (which may, for example, form part of the housing of the lithography apparatus LA, such as a mirror or the like). Generally speaking, the second body 104 may be further from the optical path, followed by the first body 102 . It will be appreciated that the second body 104 may comprise a plurality of separate parts (eg, the wall of the lithography apparatus LA). Unless stated to the contrary, the terms voltage and potential are used synonymously and interchangeably in this document.

References in this document to a reticle or reticle may be construed as references to a patterning device (reticle or reticle being examples of a patterning device) and the terms are used interchangeably. In particular, the term reticle assembly is synonymous with the reticle assembly and the patterning device assembly.

Although specific reference may be made herein to embodiments of the invention in the context of lithography equipment, embodiments of the invention may be used in other equipment. Embodiments of the invention may form part of photomask inspection equipment, metrology equipment, or any equipment that measures or processes items such as wafers (or other substrates) or photomasks (or other patterned devices). Such equipment may generally be referred to as lithography tools.

The term "EUV radiation" may be considered to cover electromagnetic radiation having a wavelength in the range of 4 nm to 20 nm, for example in the range of 13 nm to 14 nm. EUV radiation may have a wavelength less than 10 nm, for example in the range of 4 nm to 10 nm, such as 6.7 nm or 6.8 nm.

Although specific reference may be made herein to the use of lithography equipment in IC fabrication, it should be understood that the lithography equipment described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

While specific embodiments of the invention have been described, it should be understood that the invention may be practiced otherwise than as described. The above description is intended to be illustrative and not restrictive. Accordingly, it will be apparent to those skilled in the art that modifications of the invention as described may be made without departing from the scope and scope of the claims as set forth below. 1. A lithography apparatus comprising: a plurality of optical elements defining an optical path, the plurality of optical elements being configured to receive a radiation beam; projecting the radiation beam onto a reticle for patterning the radiation beam and patterning the radiation beam on a substrate an image formed on the reticle; a first body proximate the optical path; a second body proximate the optical path; a voltage supply configured to apply a potential difference across the first body and the second body; wherein the first body The second body and/or the voltage supply are configured to control the flux and/or energy distribution of ions incident on the first body from the plasma formed in the optical path by the radiation beam. 2. The lithography apparatus of clause 1, wherein the first body and the second body are configured such that the electrical conductance between the first body and the plasma is significantly less than the electrical conductance between the second body and the plasma. 3. The lithography apparatus of clause 1 or 2, wherein the second body defines a textured surface facing the optical path. 4. The lithography equipment of item 3, wherein the textured surface is a corrugated surface. 5. The lithography apparatus of any one of the preceding items, further comprising a mechanism for generating a conductive medium between the optical path and the second body. 6. The lithography apparatus of clause 5, wherein the mechanism for generating the conductive medium includes a voltage supply configured to generate a plasma between the optical path and the second body. 7. The lithography apparatus of clause 5 or 6, wherein the means for generating the conductive medium includes an electron source configured to increase the density of electrons between the optical path and the second body. 8. A lithography apparatus as in any one of clauses 5 to 7, wherein the means for generating the conductive medium comprises a radiation source configured to generate radiation propagated between the optical path and the second body. 9. The lithography apparatus of any one of clauses 5 to 8, wherein the second body includes a portion adjacent to the optical path. 10. The lithography apparatus of clause 9, wherein the portion adjacent to the optical path extends at least partially around the optical axis of the optical path. 11. A lithography apparatus as in any one of the preceding clauses, wherein the voltage supplier is configured to apply a bias potential to the first body and the second body to ground. 12. The lithography apparatus of any one of clauses 1 to 10, wherein the voltage supplier is configured to apply a bias potential to the second body and the first body is grounded. 13. A lithography apparatus as in any one of the preceding clauses, wherein the second host system is formed of a material resistant to etching by plasma. 14. The lithography equipment according to any one of the preceding items, wherein the second main system is formed of tungsten. 15. A lithography apparatus as in any one of the preceding clauses, wherein the voltage supplier is configured to apply a potential difference across the first body and the second body such that the energy of the ions incident on the first body from the plasma is distributed in to a extent that results in etching of contaminants on the surface of the first body and results in minimal etching of the bulk material of the first body. 16. A lithography apparatus as in any one of the preceding clauses, wherein the voltage supply is configured to apply an AC potential difference across the first body and the second body. 17. A lithography apparatus as in any one of the preceding clauses, wherein the voltage supply is configured such that the rate of change of potential across the plasma sheath of the plasma is small most of the time. 18. A lithography apparatus as in any one of the preceding clauses, wherein the potential difference alternates between a positive part (in which the first host system is positively biased) and a negative part (in which the first host system is negatively biased). 19. The lithography apparatus of clause 16 or 18, wherein the average value of the potential difference applied across the first body and the second body is non-zero. 20. A lithography apparatus as in any of the preceding clauses, when directly or indirectly dependent on clause 16 or 18, in which the duty cycle of the potential difference applied across the first body and the second body is such that the negative portion The ratio of the duration to the duration of the positive part is greater than 0.9. 21. Lithography apparatus as in any of the preceding clauses, when directly or indirectly dependent on clause 18, wherein the magnitude of the potential difference applied across the first body and the second body increases during the negative portion. 22. Lithography apparatus as specified in any of the preceding clauses, when directly or indirectly dependent upon clause 16 or 18, in which the frequency of the potential difference applied across the first body and the second body is less than 400 kHz. 23. The lithography equipment according to any of the preceding items, wherein the first body and/or the second body are connected to the voltage supply via a matching box or a capacitor. 24. Lithography apparatus as in any one of the preceding clauses, wherein the apparatus includes a third body proximate the optical path, wherein the third body is configured to be at ground potential or to be at floating potential, as appropriate. 25. The lithography equipment according to any one of the preceding clauses, wherein the equipment includes a diode electrically connected to the second body. 26. A lithography apparatus as in any one of the preceding clauses, wherein the apparatus is configured to provide the first body at a floating potential, a ground potential, or at another bias potential relative to ground. 27. A method of controlling the flux and/or energy distribution of ions incident on a first body in a lithography apparatus, the method comprising: guiding a radiation beam along an optical path in the lithography apparatus, the first body being close to the optical path; and applying a potential difference across the first body and a second body also proximate the optical path to control the flux of ions incident on the first body from the plasma formed in the optical path by the radiation beam and /or energy distribution. 28. The method of clause 27, wherein the first body and the second body are configured such that the electrical conductance between the first body and the plasma is significantly less than the electrical conductance between the second body and the plasma. 29. The method of clause 27 or 28, further comprising creating a conductive medium between the optical path and the second body. 30. The method of clause 29, wherein generating the conductive medium includes generating a plasma between the optical path and the second body. 31. The method of clause 29 or 30, wherein producing the conductive medium includes increasing the density of electrons between the optical path and the second body. 32. A method as in any one of clauses 29 to 31, wherein generating the conductive medium includes directing radiation for propagation between the optical path and the second body. 33. The method of any one of clauses 27 to 32, wherein applying the potential difference across the first body and the second body includes applying a bias potential to the first body and grounding the second body. 34. The method of any one of clauses 27 to 32, wherein applying the potential difference across the first body and the second body includes applying a bias potential to the second body and grounding the first body. 35. A method as in any one of clauses 27 to 34, wherein the second host system is formed from a material resistant to etching by plasma. 36. The method of any one of clauses 27 to 35, wherein the second main system is formed of tungsten. 37. The method of any one of clauses 27 to 36, wherein applying a potential difference across the first body and the second body is such that the energy of ions from the plasma incident on the first body is distributed on the surface of the first body causing The etching of contaminants on the first body results in minimal etching of the bulk material of the first body. 38. The method of any one of clauses 27 to 37, wherein applying a potential difference across the first body and the second body includes applying an AC potential difference across the first body and the second body. 39. The method of any one of clauses 27 to 38, wherein applying a potential difference across the first body and the second body is such that the rate of change of potential across the plasma sheath of the plasma is small most of the time. 40. A method as in any one of clauses 27 to 39, wherein the potential difference alternates between a positive part (in which the first host system is positively biased) and a negative part (in which the first host system is negatively biased). 41. The method of clause 38 or 40, wherein the average value of the potential difference applied across the first body and the second body is non-zero. 42. The method of any one of clauses 27 to 41, when depending directly or indirectly on clause 38 or 40, wherein the duty cycle of the potential difference applied across the first body and the second body is such that the negative part The ratio of the duration to the duration of the positive part is greater than 0.9. 43. The method of any one of clauses 27 to 42, when depending directly or indirectly on clause 37, wherein the magnitude of the potential difference applied across the first body and the second body increases during the negative portion. 44. The method of any one of clauses 27 to 43, when directly or indirectly dependent on clause 19 or 31, wherein the frequency of the potential difference applied across the first body and the second body is less than 400 kHz. 45. The method of any one of clauses 27 to 44, wherein the first body and/or the second body are connected to the voltage supply via a matching box or a capacitor. 46. The method of any one of clauses 27 to 45, wherein the method further includes providing a third body at ground potential or at floating potential. 47. The method of any one of clauses 27 to 46, wherein the method further comprises providing a diode electrically connected to the second body thereby biasing the second body relative to ground. 48. The method of any one of clauses 27 to 47, wherein the method includes providing the first body at a floating potential, a ground potential, or at another bias potential relative to ground.

1: Laser 2: Laser beam 3: Fuel emitter 4: Plasma formation area 5: Near normal incidence radiation collector 6: Intermediate focus 7: Plasma 8: Opening 9: Enclosing structure 10: Faceting field Mirror device/optical element/mirror 11: faceted pupil mirror device/optical element/mirror 13: mirror/optical element 14: mirror/optical element 15: multiplication mask assembly/film assembly 17: film Frame 19: Surface film 100: Plasma 102: First body/first component 104: Second body 106: Plasma sheath 108: Voltage supplier/voltage source 110: Capacitor 112: Mechanism 114: Ionizing radiation source 116: Section Three subjects 200: specific waveform 202: positive part 204: negative part 300: method 302: step 304: step B: extreme ultraviolet (EUV) radiation beam/patterned radiation beam IL: illumination system LA: lithography equipment MA: pattern Chemical device/reducing mask MT: support structure PS: projection system R ₁ : first resistor R ₂ : second resistor SO: radiation source V _b : bias potential/periodic potential difference W: substrate WT: substrate stage

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: - Figure 1 is a schematic illustration of a lithography system including lithography equipment and a radiation source; - Figure 2 is a schematic illustration of a lithography apparatus including two bodies close to an optical path and a voltage supply according to an embodiment of the present disclosure; - Figure 3 shows an exemplary waveform of an AC bias potential that may be applied across the first body and the second body in the configuration shown in Figure 2; and - Figure 4 is a schematic illustration of a method according to an embodiment of the present disclosure that can be performed using the lithography apparatus shown in Figure 2. - Figure 5 is a schematic illustration of a lithography apparatus including three bodies close to an optical path and a voltage supply, according to an embodiment of the present disclosure.

100:Plasma

102: First body/first component

104:Second subject

106: Plasma sheath

108:Voltage supplier/voltage source

110:Capacitor

112:Organization

114: Ionizing radiation source

R ₁ : first resistor

R ₂ : second resistor

V _b :bias potential/periodic potential difference

Claims (16)

A lithography equipment including: A plurality of optical elements defining an optical path, the plurality of optical elements configured to receive a radiation beam, project the radiation beam onto a doubling reticle to pattern the radiation beam and form the doubling beam on a substrate. An image of a telescope; a first body proximate to the optical path; a second body proximate to the optical path; and a voltage supplier configured to apply a potential difference across the first body and the second body; wherein the first body, the second body and/or the voltage supply are configured to control a flux of ions incident on the first body from a plasma formed in the optical path by the radiation beam and/or energy distribution. The lithography apparatus of claim 1, wherein the first body and the second body are configured such that an electrical conductance between the first body and the plasma is significantly smaller than an electrical conductance between the second body and the plasma. Conductance. The lithography apparatus of Claim 1 or Claim 2, further comprising a mechanism for generating a conductive medium between the optical path and the second body, the mechanism comprising a voltage supply, the voltage supply passing through configured to generate a plasma between the optical path and the second body, and/or comprising an electron source configured to increase a density of electrons between the optical path and the second body, and/or includes a radiation source configured to generate radiation propagated between the optical path and the second body. The lithography apparatus of claim 3, wherein the second body includes a portion adjacent to the optical path, the portion extending at least partially around an optical axis of the optical path. The lithography apparatus of claim 1 or claim 2, wherein the voltage supplier is configured to apply a bias potential to the first body and ground the second body, or wherein the voltage supplier is configured to A bias potential is applied to the second body and the first body is grounded. The lithography apparatus of claim 1 or claim 2, wherein the voltage supplier is configured to apply a potential difference across the first body and the second body such that ions from the plasma incident on the first body An energy distribution is within a range that results in etching of contaminants on a surface of the first body and results in minimal etching of a block of material of the first body. The lithography apparatus of claim 1 or claim 2, wherein the voltage supplier is configured to apply an AC potential difference across the first body and the second body. The lithography apparatus of claim 1 or claim 2, when directly or indirectly attached to claim 7, wherein a duty cycle of the potential difference applied across the first body and the second body is such that the negative part A ratio of the duration to the duration of the positive part is greater than 0.9. The lithography apparatus of claim 1 or claim 2, wherein the apparatus includes a third body proximate the optical path, optionally wherein the third body is configured to be at ground potential or to be at floating potential. A method of controlling the flux and/or energy distribution of ions incident on a first body in a lithography apparatus, the method comprising: directing a radiation beam along an optical path in the lithography apparatus, the first body being proximate to the optical path; and A potential difference is applied across the first body and a second body also proximate the optical path to control the passage of ions incident on the first body from a plasma formed in the optical path by the radiation beam. quantity and/or energy distribution. The method of claim 10, wherein the first body and the second body are configured such that an electrical conductance between the first body and the plasma is significantly less than an electrical conductance between the second body and the plasma. The method of claim 10 or claim 11, further comprising generating a conductive medium between the optical path and the second body, wherein generating a conductive medium includes generating a plasma between the optical path and the second body, and/or wherein creating a conductive medium includes increasing a density of electrons between the optical path and the second body, and/or Creating a conductive medium includes directing radiation to propagate between the optical path and the second body. The method of claim 10 or claim 11, wherein applying a potential difference across the first body and a second body includes applying a bias potential to the first body and grounding the second body, or wherein across the Applying a potential difference between the first body and a second body includes applying a bias potential to the second body and grounding the first body. The method of claim 10 or claim 11, wherein applying a potential difference across the first body and a second body includes applying an AC potential difference across the first body and the second body. The method of claim 14, wherein a duty cycle of the potential difference applied across the first body and the second body is such that a ratio of the duration of the negative part to the duration of the positive part is greater than 0.9. The method of claim 10 or claim 11, wherein the method further includes providing a third body at ground potential or at floating potential.